The water-hammer-strength test of glass bottles is defined by the “water-hammer test method” prescribed by Japan Glass Bottle Association. This defines the water-hammer test method for packaged glass bottles.
FIG. 18 is a diagram for explaining a test according to the above-mentioned definition. This test uses a drop testing machine 20 defined by “JIS Z 0202”. A case of a lower dummy 23 (the same as a sample) is placed on a drop surface 21 (an iron plate having a thickness of 20 mm or more), and a case of a sample 24 is disposed thereon. A case of an upper dummy 25 (the same as the sample) is placed on a sample stage 22 of the drop testing machine 20. The lower dummy 23, the sample 24, and the upper dummy 25 are bottles filled with a predetermined amount of formal content according to a formal filling method and sealed with a predetermined cap, or other equivalents, which are packaged in a predetermined manner. Each case accommodates many glass bottles.
The sample stage is set at a predetermined drop height (the distance between the bottom surface of the upper dummy and the top surface of the sample), and the upper dummy is dropped onto the sample from a drop height of, for example, at first, 30 cm. The drop tests are repeated until a predetermined drop height is reached to see if any one of the glass bottles in the sample is damaged, while increasing the drop height by an increment of 5 cm (for a drop height of 60 cm or more, an increment of 10 cm is applied). The drop height at which any one of the sample bottles is damaged is regarded as the water hammer strength.
When the upper dummy 25 falls onto the sample 24, the case of the lower dummy 23 is deformed, and the glass bottles in the sample 24 are abruptly pushed downward. However, the content (liquid) of the glass bottles remains at the original position due to inertia, creating vacuum portions (vacuum bubbles) at the bottoms of the bottles. Immediately after that, the content abruptly falls onto the bottoms, which are in a vacuum state, causing a water hammer effect.
The “water-hammer test method” prescribed by Japan Glass Bottle Association is for measuring the water hammer strength of packaged glass bottles and is not for testing the water hammer strength of glass bottles themselves (the water hammer strength changes depending on the specifications of packages). Furthermore, because the test cannot be performed without preparing cartons, the test requires many products (about 10 cases). Thus, the water hammer strength evaluation cannot be performed in the test production in the design phase of bottle parisons. Moreover, the test requires considerable labor for tasks such as lifting the cartons, checking the bottles for damage, cleaning up of the damaged bottles, checking the cartons for damage, etc.
PTL 1 below proposes a technique that solves the above-described problems, enables measurement of the water hammer strength of glass bottles themselves with relative ease, and enables strength evaluation in the test production (in the design phase of bottle parisons).
This is a method for testing the water hammer strength of a glass bottle, in which holding element is provided on a fixing stage via a cushion member, the holding element holds the bottle filled with content and sealed with a cap at a position above the center of gravity thereof so as to suspend the bottle in the air, a weight is directly or indirectly dropped onto the cap to apply an impact to the bottle, and the weight is repeatedly dropped while gradually increasing the drop energy, thereby testing the water hammer strength of the bottle on the basis of the drop energy of the weight when the bottle is damaged.
When the weight is directly or indirectly dropped onto the cap, the cushion member is deformed, and the bottle is abruptly pushed downward, causing a water hammer effect. If the weight is dropped onto the bottle held at a position above the center of gravity thereof and suspended, the drop energy of the weight acts on the bottle efficiently. Thus, the drop energy of the weight is strongly associated with the impact applied to the bottle, making it possible to accurately know the water hammer strength of the bottle on the basis of the drop energy of the weight when the bottle is damaged.